Mail sent to the second domain I set up bounces with the previously mentioned relay error
(I have entered 2 domains in mySQL - sailmaster.nl and quitter.nl. The hostname of my server is magistervela.sailmaster.nl.) The quitter.nl mail bounces.

It just does not seem to make the new dir.
FYI: I did yet another clean install, still running in to the problem. Then I added Virtual Hosting With Proftpd And MySQL as described in the tutorial and there everything works like a charm. I guess I am missing something, but really don't know what...